(a) The Field of the Invention
The present invention relates to a process for the dissolution of cellulose in organic solvents, to solutions obtained by said process, and to a process for the production of formed bodies of regenerated cellulose from said solutions.
The art has devoted considerable attention to the problem of preparing cellulose solutions in organic solvents, capable of yielding formed bodies of regenerated cellulose, such as membranes of yarns, by coagulation. Regenerated cellulose membranes and yarns are presently prepared on a large industrial scale through chemical processes, such as e.g. the so-called viscose process, based on the formation of cellulose xantogenate, which has several well-known drawbacks.
(b) The State of the Art
Binary or tertiary systems capable of dissolving cellulose have been described in the literature, but these have a purely experimental interest or at least are not suitable for industrial application.
Such a system is constituted of paraformaldehyde or formaldehyde and dimethylsulphoxide (DMSO), in which system cellulose is dissolved through the formation of derivatives the structure whereof is not precisely known and which are generally regarded as methylol derivatives. The resulting solutions, however, are difficult to coagulate to generate formed bodies. In U.S. Pat. No. 4,022,631 a method for regenerating the cellulose from said solutions is described and claimed, which is characterized by the use of alkaline coagulating agents, e.g. ammonia, but said method too is not suitable for industrial production.
Other organic solvents are known which are preferable to DMSO for economical and process reasons and which are already employed for making spinnable solutions e.g. of acrylic polymers. The most commonly used among them is dimethylformamide (DMF) but others, in particular dimethylacetamide, have been employed successfully in spinning acrylic polymers. The relevant chemical literature however teaches that these solvents cannot be used in place of DMSO inasmuch as the cellulose is not soluble in a system composed of paraformaldehyde or formaldehyde and DMF, dimethylacetamide, and the like.